Animation is rendered in Eevee instead of cycles
This happened to me, here is how I fixed it.

I rendered an animation in EEVEE to see what it was like and then created a video using the video sequencer.

Next day, I decided to do a Cycles render, but regardless of settings it always seemed to render an EEVEE render for both single image and animation.

Then I realised, I still had the EEVEE png files referenced in the Video Sequencer.

I deleted the strip, and then Hey Presto, I got Cycles rendering back!